Catechin is reported to possess an α-amylase-activity-inhibiting effect as one of its properties (see, for example, Patent Document 1). In order for such a physiological effect to materialize, catechin needs to be ingested in large amounts, so there has been a strong demand for a technology making it possible to obtain a beverage containing catechin in high concentration.
As one example among such technologies, there is a method characterized in that catechin is added in a dissolved form to a beverage by making use of a tea extract (e.g., the concentrate of a green tea extract), However, this method is known to impair the quality of a beverage, depending on the kind of a beverage to which catechin is to be added in high concentration. For example, a tea-based beverage or a non-tea-based beverage (e.g., a carbonated beverage) is susceptible to the residual bitterness and astringency intrinsic to caffeine and green tea, thus causing its commercial value to be considerably damaged.
Adsorption methods (Patent Documents 2 to 4), extraction methods (Patent Documents 5 to 6) and the like are known for removing impurities, like caffeine, from a tea extract.
In these methods, an organic solvent may be used if it is desired to increase the content of non-polymer catechins in a tea extract, but this is problematic because the recovery rate is poor from the industrial viewpoint.
As a method for improving the color tone of a tea extract, it is known to use an antibacterial deodorant obtained by causing activated carbon to act on the tea extract in the presence of a cyclodextrin to adsorb color components on the activated carbon for their elimination (Patent Document 7). This method, however, is difficult to use in the case of a catechin preparation required for drinking.
It is known that the flavor and taste of a green tea extract can be improved by controlling the percentage of non-gallates in non-polymer catechins (see Patent Document 8). In addition, as disclosed in Patent Document 9, it is possible to reduce the amount of the gallate catechin responsible for bitterness, by a method that applies tannase treatment to gallate catechins and converts a part or the entire part of them into gallic acid to obtain a mixture of catechins and gallic acid. However, this method is meant to control the percentage of non-gallates by conducting tannase treatment, so that the obtained flavor or taste was not satisfactory due to the remaining enzyme (tannase) and the formation of gallic acid through hydrolysis of the gallates.
An efficient technology already exists for the production of a tea extract with gallates contained at a high percentage (see Patent Document 10), but there is no efficient technology known for the production of a tea extract containing non-gallates at a high percentage. On the other hand, there is a technology known for treating a tea extract with a synthetic adsorbent and collects unadsorbed components (see Patent Document 11). This technology is nonetheless not suited for applications such as a beverage, because of the residual flavor and taste intrinsic to tea as well as its strong bitterness.
There is yet another technology known for loading a green tea extract on a column packed with a synthetic adsorbent to effect adsorption and then allowing it to be desorbed with two aqueous ethanol solutions of different concentrations (see Patent Document 12). This technology is meant to remove caffeine and impurities while maintaining the catechin composition through the treatment, so the improvement effect on flavor and taste attributable to the percentage of non-gallates is marginal.
Patent Document 1: JP-A-03-133928
Patent Document 2: JP-A-05-153910
Patent Document 3: JP-A-08-109178
Patent Document 4: JP-A-2002-335911
Patent Document 5: JP-A-01-289447
Patent Document 6: JP-A-59-219384
Patent Document 7: JP-A-2001-299887
Patent Document 8: JP-A-2004-321105
Patent Document 9: JP-A-2004-222719
Patent Document 10: JP-A-2006-036645
Patent Document 11: JP-A-2005-170871
Patent Document 12: JP-A-2006-008580